Adding SWIG Java wrappers to LightGBM (#1223)

* Adding Java wrappers to LightGBM by updating CMakeLists and adding SWIG file

* Set SWIG generation to OFF by default

* Added -package option to SWIG_FLAGS

* Fixed jar structure to have class files in proper location

* removed link with OpenMP flags

CMakeLists.txt

@@ -11,6 +11,7 @@ PROJECT(lightgbm)
 OPTION(USE_MPI "MPI based parallel learning" OFF)
 OPTION(USE_OPENMP "Enable OpenMP" ON)
 OPTION(USE_GPU "Enable GPU-acclerated training (EXPERIMENTAL)" OFF)
+OPTION(USE_SWIG "Enable SWIG to generate Java API" OFF)
 
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.8.2")
@@ -28,6 +29,25 @@ if(APPLE)
     OPTION(APPLE_OUTPUT_DYLIB "Output dylib shared library" OFF)
 endif()
 
+if(USE_SWIG)
+  find_package(SWIG REQUIRED)
+  find_package(Java REQUIRED)
+  find_package(JNI REQUIRED)
+  include(UseJava)
+  include(UseSWIG)
+  set(SWIG_CXX_EXTENSION "cxx")
+  set(SWIG_EXTRA_LIBRARIES "")
+  set(SWIG_JAVA_EXTRA_FILE_EXTENSIONS ".java" "JNI.java")
+  set(SWIG_MODULE_JAVA_LANGUAGE "JAVA")
+  set(SWIG_MODULE_JAVA_SWIG_LANGUAGE_FLAG "java")
+  set(CMAKE_SWIG_OUTDIR "${CMAKE_CURRENT_BINARY_DIR}/java")
+  FILE(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/com/microsoft/ml/lightgbm/linux/x86_64")
+  include_directories(Java_INCLUDE_DIRS)
+  include_directories(JNI_INCLUDE_DIRS)
+  include_directories($ENV{JAVA_HOME}/include)
+  include_directories($ENV{JAVA_HOME}/include/linux)
+endif(USE_SWIG)
+
 if(USE_MPI)
     find_package(MPI REQUIRED)
     ADD_DEFINITIONS(-DUSE_MPI)
@@ -127,6 +147,18 @@ file(GLOB SOURCES
 add_executable(lightgbm src/main.cpp ${SOURCES})
 add_library(_lightgbm SHARED src/c_api.cpp src/lightgbm_R.cpp  ${SOURCES})
 
+if(USE_SWIG)
+  set_property(SOURCE swig/lightgbmlib.i PROPERTY CPLUSPLUS ON)
+  LIST(APPEND swig_options -package com.microsoft.ml.lightgbm)
+  set_property(SOURCE swig/lightgbmlib.i PROPERTY SWIG_FLAGS "${swig_options}")
+  swig_add_module(_lightgbm_swig java swig/lightgbmlib.i)
+  swig_link_libraries(_lightgbm_swig _lightgbm)
+  add_custom_command(TARGET _lightgbm_swig POST_BUILD
+    COMMAND "${Java_JAVAC_EXECUTABLE}" -d . java/*.java
+    COMMAND cp "${PROJECT_SOURCE_DIR}/*.so" com/microsoft/ml/lightgbm/linux/x86_64
+    COMMAND "${Java_JAR_EXECUTABLE}" -cf lightgbmlib.jar com)
+endif(USE_SWIG)
+
 if(MSVC)
     set_target_properties(_lightgbm PROPERTIES OUTPUT_NAME "lib_lightgbm")
 endif(MSVC)

swig/lightgbmlib.i

@@ -0,0 +1,99 @@
+/* lightgbmlib.i */
+%module lightgbmlib
+%ignore LGBM_BoosterSaveModelToString;
+%{
+/* Includes the header in the wrapper code */
+#include "../include/LightGBM/export.h"
+#include "../include/LightGBM/utils/log.h"
+#include "../include/LightGBM/c_api.h"
+%}
+
+/* header files */
+%include "../include/LightGBM/export.h"
+%include "../include/LightGBM/c_api.h"
+%include "cpointer.i"
+%include "carrays.i"
+
+%inline %{
+  char * LGBM_BoosterSaveModelToStringSWIG(BoosterHandle handle,
+					   int num_iteration,
+					   int64_t buffer_len,
+					   int64_t* out_len) {
+    char* dst = new char[buffer_len];
+    int result = LGBM_BoosterSaveModelToString(handle, num_iteration, buffer_len, out_len, dst);
+    if (result != 0) {
+      return nullptr;
+    }
+    return dst;
+  }
+%}
+
+%pointer_functions(int, intp)
+%pointer_functions(long, longp)
+%pointer_functions(double, doublep)
+%pointer_functions(float, floatp)
+%pointer_functions(int64_t, int64_tp)
+%pointer_functions(int32_t, int32_tp)
+
+%pointer_cast(int64_t *, long *, int64_t_to_long_ptr)
+%pointer_cast(int64_t *, double *, int64_t_to_double_ptr)
+%pointer_cast(int32_t *, int *, int32_t_to_int_ptr)
+%pointer_cast(long *, int64_t *, long_to_int64_t_ptr)
+%pointer_cast(double *, int64_t *, double_to_int64_t_ptr)
+%pointer_cast(double *, void *, double_to_voidp_ptr)
+%pointer_cast(int *, int32_t *, int_to_int32_t_ptr)
+%pointer_cast(float *, void *, float_to_voidp_ptr)
+
+%array_functions(double, doubleArray)
+%array_functions(float, floatArray)
+%array_functions(int, intArray)
+%array_functions(long, longArray)
+
+/* Custom pointer manipulation template */
+%define %pointer_manipulation(TYPE,NAME)
+%{
+  static TYPE *new_##NAME() { %}
+  %{  TYPE* NAME = new TYPE; return NAME; %}
+  %{}
+
+  static void delete_##NAME(TYPE *self) { %}
+  %{  if (self) delete self; %}
+  %{}
+  %}
+
+TYPE *new_##NAME();
+void  delete_##NAME(TYPE *self);
+
+%enddef
+
+%define %pointer_dereference(TYPE,NAME)
+%{
+  static TYPE NAME ##_value(TYPE *self) {
+    TYPE NAME = *self;
+    return NAME;
+  }
+%}
+
+TYPE NAME##_value(TYPE *self);
+
+%enddef
+
+%define %pointer_handle(TYPE,NAME)
+%{
+  static TYPE* NAME ##_handle() { %}
+  %{ TYPE* NAME = new TYPE; *NAME = (TYPE)operator new(sizeof(int*)); return NAME; %}
+  %{}
+%}
+
+TYPE *NAME##_handle();
+
+%enddef
+
+%pointer_manipulation(void*, voidpp)
+
+/* Allow dereferencing of void** to void* */
+%pointer_dereference(void*, voidpp)
+
+/* Allow retrieving handle to void** */
+%pointer_handle(void*, voidpp)
+